Wheat starch process



WHEAT STARCH PROCESS product.

Patented Apr. 8, 1947 PATENT OFFICE ltobert w. Callaghan and Richard H. seaming,

Minneapolis, Minn., assignor to General Mills,

t Inc., a corporation of Delaware Application August 4, 1943, Serial No. 497,408

1:: Claims.

tpresent invention relates to a process of separating starch from a starch slurry, and more particularly..the separation of wheat starch from By means of the present invention it is possible to: separate'fand' recover a, very high percentage of .the'jstarch contalned in a slurry, particularly slurrles resulting from the separation of flour, farina, meal and other wheat products into gluten dstarch- It is therefore a primary object of the present invention to provide a process of recovering starch from a starch slurry so as to increase the yield and at the same time improve the purity of the It is a further object of the present invention to provide a process for the separation of wheat into starch and gluten while permitting the recovery of starch and gluten in relatively pure form and with high yields.

Theseand other objects of the invention will be apparent from the following description of the invention with particular reference to the .drawings which represent flow sheets of various emhodiments of the invention.

' Broadly, the process involves forming a dough containing starch, gluten and water, washing the dough with water to extract the starch from the gluten, and recovering the starch from the resultant slurry. As to the formation, working, and

extraction of the dough, it is preferred to employ the process set forth in detail in the co-pending application of Callaghan and Elverum, Serial No. 383,678, filed March 17, 1941. This process involves the formation of a dough containing starch, gluten and water, the hydration of the dough, and the working of the dough until the gluten has become substantially completely agglomerated. By this it is meant that the dough is composed of a network of gluten fibers, with the starch particles held in the interstices of the network. By obtaining this continuous network of gluten fibers before washing, the dough mass clings together during the washing operation and, as a result, there is practically no tendency for small particles of gluten to break off and separate with the starch After the gluten has become agglomerated, the dough mass is discharged into a rotary drum and tumbled about relatively sharp. projections in the drum in the presence of water to work the starch from the dough to yield a, starch slurry. Thi slurry is separated from the gluten mass by means of a suitable screen or sieve. The-gluten. discharged from the extracting drum may then be washed in a suitable wash- (Cl. 12'I--87) counter-current now, being introduced first into the second washer, then into the first washer, and finally into the extractor.

In general, the starch slurry obtained from the extractor is subjected to a sequence of steps, namely thickening the slurry to condition it for recoveryof starch, separating the slurry into a concentrated starch slurry and a thin slurry composed of bran, starch and water and stripping bran and starch from the thin slurry. These functions are performed in the respective flow sheets in different manner-s. Each particular flow has advantages as will be pointed out in the specific description of each.

In Fig. l the starch slurry removed from the extractor may be passed over a screen for the removal of the larger bran particles. The slurry passing through the screen is then run to a settler which may :be of conventional type having a discharge for solids at the bottom and a rake for conveying the settled solids to the discharge. If the settler is of suificient capacity, the overflow from the settler will be substantially free from suspended solids and will contain only the soluble matter extracted from the flour. This soluble matter may be recovered or may be employed wherever a material having the properties of this material is suitable.

It has been found that the slurry taken off the extractor is composed of relatively large starch particles and also fine starch particles and bran. The fine starch is usually of such a small particle size that it could not be settled within a, reasonable time if independent settling of the individual particles had to be relied on. It has been found, however, that the slurry introduced into the settler flocculates, the bran particles appearing to assist in the formation of a fioc which, as it settles, sweeps the slurry clear of all suspended particles.

By this means it is possible to. remove practically points.

'1,923,455 has been found satisfactory for this assist in perfecting the separation in the cen-l,

trifuge. Likewise, this machine provides for the introduction of wash water into the centrifuge which is usually mixed with the internally recycled concentrated solids. In the drawings the centrifuge is illustrated as-a square and is shown with the feed entering the top of the centrifuge. The concentrated solids or underflow are indi cated by the letter U while the light eiliuent or overflow is indicated by the letter 0. Wash water is shown being introduced into the bottom of the illustrated centrifuge. Likewise, the internally recycled concentrated solids are shown being introduced at the same point as the wash water.

The preliminary concentrating of the solids in the settler has been found to be highly important preparatory to centrifugal separation. Asoluble foaming agent of unknown character appears to be present in wheat and this foaming agent finds its way into the starch slurry. Centrifugal separation of a dilute starch slurryjusually results in foaming difliculties. When a higher concentration starch slurry is subjected to centrifugal separation, however, these difficulties are not encountered. Likewise, thickening. of the feed to the centrifuge increases centrifuge capacity and increases emciency of starch purification.

The underflow from the centrifuge is a. flowable slurry composed essentially of starch and water.

This slurry may be run over a screen to remove any remaining bran particles that may have found their way into the purified slurry. After screening, the slurry may be dewatered, for example, by filtering and the filter-cake dried to recover a, pure starch. For the purpose of filtration, it is preferred to employ a continuous filter in which the starch slurry may be dewatered and washed. The filtrate may be recovered separately from the wash water or may be mixed with the wash water and recycled to the No. 1 or No. 2 washer, or both, depending on the nature 'of the filtrate and on the type of gluten product desired.

The overflow from the centrifuge is run over a bran screen for the further removal of bran, after which the overflow is returned to the settler. This overflow contains part of the starch, as a perfect separation is not obtained in the centrifuge. This starch is then returned to the settling operation and part of it will be recovered in a 'pure form in a subsequent cycle.

It will be apparent from. the drawing that bran particles may be removed from the process at a number of points. The largest particles are removed on the first bran screen. In flour, however, many of the bran particles approach the size of the starch granules. Accordingly, many of them pass .through this first bran screen. The bran particles, however, tend to swell on prolonged contact with water and as a result a stream withdrawn from the centrifuge will be found to contain bran particles which have swollen to a size permitting their being screened off. While it is preferred to remove substantial quantities of bran on the first bran screen, this may be omitted and. the bran removed at the other In. this flow diagram the thickening step ocours in the settler, the separating step in the 'ered in a subsequent cycle.

centrifuge, and the stripping of the starch from the centrifuge overflow is' performed in a subse-' quent cycle in the settler.

In Fig. 2 the starch slurry is likewise screened,

settled and centrifuged in a manner similar to Fig. 1. The underflow from the centrifuge is similarly processed as injig. l.

viously, the material introduced into the centrifuge contained essentially large starch particles, bran and fine starch. Separation in the centrifuge was effected by means ofthe density and size differential of the large starch over the remaining bran and fine starch, the latter two having essentially the same settling rate. It has been found that while the bran and fine starch cannot be satisfactorily separated by ordinary settling, because of their tendenc to flocculate,

they can be separated by taking advantage of the size and density differential in diluted slurries which permits these substances to be separated by hydraulic classification. The overflow from the centrifuge is shown being introduced into a hydraulic classifier in which the relatively larger bran particles settle to'the bottom and are removed. The flne starch particles do not settle as rapidly and are washed over the top into the eiiiuent launder. The overflow from this classifler is composed essentially of a dilute fine starch slurry which is recycled to the No. 1 washer which permits part of this starch to be recov- Th6 bran removed from the bottom of the first classifier contains some starch and accordingly is further purifiedposed of to waste. The overflow from the second classifier may be introduced into the first classifier as the liquid against which the bran particles must settle. Overflow liquid from'the settler may be used as the water introduced into the second classifier against which fine starch particles in the bran slurry must rise to be separated from the settling bran particles. Part of the centrifuge overflow is shown being recycled to the settler for recovery of starch in that manner rather than the entire amount of overflow being recycled to the washer. i I

In this operation the solubles are found to build up in the system to a considerable concentration and accordingly it is desirable to bleed oil a relatively concentrated solution of solubles from the settler overflow. These solubles are valuable and since a reasonably high concentration of them can be obtained in this liquid, the low cost of water removal makes recovery desirable. It will be noted that the recycling of the fines from the hydraulic classifier back to the gluten washer greatly increases the time during which the starch is subject to fermentation. For this reason it is preferred to employ an antiseptic in the system. For this purpose, the nitrltes referred to in the application of Richard H. Schilling, Serial No. 497,407, filed of even date here:-

with, have been found highly desirable.. They v The overflow from the centrifuge is composed principally of k water, bran and fine starch. As was stated prebringing the pH to a point below about 4.5 and thus interfering with settling.

The recycling of nitrites into contact with the gluten appears to make the gluten undenaturable by heat.

effecting denaturization. This is particularly desirable where an undenatured gluten is wanted. It is thus possible to obtain an undenatured gluten in a simple manner without resorting to the extraordinary precautions heretofore required. In the event that a denatured gluten is desired. the effect of the nitrite may be eliminated by the introduction of a small amount of ammonia. Likewise, it is possible to avoid the wash water in the second hydraulic classifier in place of the overflow from the settler. Thus a large part ofthe nitrite contained in the centrifuge overflow will be washed out and dis-,

charged with the bran slurry and only a trace will be recycled vwith the fine starch slurry. These starch fines are relatively free from microbial contamination and as only a relatively short time period elapses before these fines are again brought in contact with nitrite, only a It is thus possible to employ more; drastic drying conditions on the gluten without previously described manner. The overflow from the first centrifuge is run to a second centrifuge to yield a;.third underflow which is returned to the settler. The third overflow isrecycled to the gluten washers; As in Figs. 3and14, branis periodicallybled off this thirdgoverflowh The settlers-may be operated to yield a substantially clear overflow which can be recycled directly-to- ,the washer without eflecting a furthersepar a tion as is the case in l igs. 3 and 4.

In Fig. ,6 the slurry from the extractor is screened and run to a first centrifuge to yield an underflow which is then run to a second centrlfuge,- from which the underflow is run to the starch recovery system? The overflowfrom the second centrifuge is recycIedto the first centrifuge. The overflow fromthe first centrifuge is run to a hydraulic classifier where thebran is settled out and recovered. Part'of the overflow:

from the classifieris recycled to the gluten washersand part of it is diverted for the recovery of solubles. i a I In the flows shown inFigs. 2, 4, 5 and 6 where recycling is employed, it is usually desirable to employ a preservative such as the nitrite previously described.- This is Particularly important slight amount of fermentation takes place. Likewise, little fermentation is encountered in the slurry withdrawn from the extractor, as the period during which no nitrite is present, is short.

In Fig. 3 a three-stage separation is illustrated. The slurry from the extractor is screened for the removal of bran and is then'centrifu-ged. The underfiow from the first centrifuge is run through a'second centrifuge to yield a second underflow from which starch is recovered in the same manner as in the previous figure. The overflow from the second centrifuge is recycled over the bran screen and returned to the first centrifuge. The

overflow from the first centrifugeis run through a third centrifuge to yield a third underflow which is recycled to the first centrifuge and the third overflow which is discharged to waste. Usually the material discharged to wasteis sufficiently low in solubles as not to warrant its recovery.

all of it may be returned to either. In thismanner it is possible to build up. thesoluble content of the. third overflow and make it desirable to of the system can in the flows illustrated in "Figs. 2, 5 and 6 where centrifugal separation is not employed exclusively. The employment of settling requires a prolonged period of time and accordingly the possibilities of fermentation are increased. In the flow of Fig. 4 in which separation is effected by means of centrifuges exclusively, the time period is materially reduced and the extent of fermentation is materially reduced. Nevertheless, itis usually desirable to employ a preservative in this flow also. i i i It is desired to point out thatin' all of these flows, starch is recovered at a single point. There is no secondary starch product "removed from the system. Accordingly. all of the. starch is of prime purity. This is accomplished by recycling various streams containing starch to a point where the starch can b be recovered as prime starch. At the same time the bran and solubles be withdrawn and recovered asdesired. i H i i v The solubles constitute evaluable by--product. They are composed principally of soluble sugars, amylase, lactates, vitamins and growth factors, and soluble inorganic salts extracted from the flour. This material may be advantageously employed wherever a material of thisdescription is found desirable. i H

By the term gravity concentrating" asused herein, itis inte'nded to mean concentrating by difference in specific gravity and "is intended. to cover simple gravity concentratingas:well as where the effect ofgravity is multiplied as by meansofac'entrifuge. I f 1 While various modifications of the invention I have-been; disclosed in detail, it will be apparent recover. this material. 1 In this flow the third un- I derflow and the secondoverflownreJ-united and returned tothe bran screen. In this manner there is a lesser tendency for bran to build up I in the centrifuge system and accordingly the 1 periodic bran bleed-off from the" third overflow i need be less frequent.

In Fig. 5, a c nsiderably trated. ,The'screened slurry from: the extractor is run i 's settlersimilar to Fig.1. The underv that .thesameisnot limited thereto butmay be varied within thescope ofthe appended claims.

,we claim asour invention:

1. Process of preparing wheat comprises forming a dough containing wheat f to convert (said dough into a starch slurryand a gluten massgseparati'ng the starch slurryfrom the gIuten' mass, concentrating the slurry by ravity... ubiecflus ra e slu r to centrifugal separation in a separating zone, re

flowvfrbmlthisisettleris,centrifugedtd yield an underflow from which starch is 'recoveredln the.

moving starclij therefrom an. underflow' a'. thin slurry as an overflow, and recoveringadstarch which I to convert said dough into a' starch slurry and a" gluten mass, separating the starch slurry from the gluten mass, separating bran from the starch slurry, concentrating the slurry by gravity, subjecting'the concentrated slurry to centrifugal separation in a separating zone, removing starch therefrom as an underflow and a thin slurry as an overflow, and recovering additionalstarch fromthe overflow by returning at least part of it to the concentrating step and thus subjecting it to centrifugal separation in said separating zone.

3. Process of preparing wheat starch which comprises forming a dough containing wheat starch and gluten, working the dough with water to convert said dough into a starch slurry and a gluten mass, separating the starch slurry from the gluten mass, separating bran from the starch slurry, concentrating the slurry by gravity, subjecting the concentrated slurry to centrifugal separationv in a separating zone, removing starch therefrom as an underflow and a thin slurry as an overflow, and recovering additional starch from the overflow by returning at least part of it to centrifugal separation in said separating zone, in thepresence ofa further quantity of .s u Y- ,4. Process of preparing wheat starch which comprises forming av dough containing wheat starch and gluten, working the dough with water to convert said dough into a starch slurry and a glutenmass, separating the starch slurry from the glutenmass, separating bran from the starch slurry, subjecting the slurry to a gravity concentratingstep' to produce a first underflow and a first overflow, subjecting the first underflow to centrifugal separation to yield a second underflow and a second overflow, recovering starch from the second underflow, returning the second overflow to the gravity concentrating step, and subjecting the first overflow to a gravity separation to yield a third underflow and a third overflow, and recovering starch from the third underflow by returning at least part of it to the concentrating step and thus subjecting it to centrifugal separation in the presence of a further quantity of slurry.

5. Process of, preparing wheat starch which comprises forming a dough containing wheat starch and gluten, working the dough with water to convert said dough into a starch slurry and a gluten mass, .separating the starch slurry from the gluten mass, separating bran from the starch slurry, subjecting-the slurry to a gravity con-' centrating' step to' produce a first underflow and a first overflow, subjecting the first underflow to centrifugal separation to yield a second underflow and a second overflow, recovering, starch from the second underflow, returning th second overflow to the gravity concentrating step, sub- 8 a gluten mass, separating the starch slurry from the gluten mass, separating bran from the starch slurry, subjecting the slurry to a gravity concentrating step to produce a flrst underflow and a first overflow, subjecting the flrstunderflow to centrifugal separation to-yield a second'underflow and a second overflow, recovering starch from the second underflow, returning the second overflow, to the gravity concentrating step, subjecting the first overflow to'a gravity separation to yield a third underflow and a third overflow,

andwashing the gluten mass with the third a gluten mass, separating the starch slurry from the gluten mass, concentrating the slurry by gravity, subjecting the concentrated slurry to centrifugal separation in a separating zone, re-

, moving starch therefrom as an underflow and a thin slurry as an overflow, recovering additional starch from the overflow by returning at least part. of it to the concentrating step and thus subjecting it to centrifugal separation in said separating zone, removing water from the underflow, and washing the gluten mass with the wate separated from the underflow.

8. Process of preparing wheat starch which comprises forming a dough containing wheat starch and gluten, working the dough with water to convert said dough into a starch slurry and a gluten mass, separating the starch slurry from the gluten mass, subjecting the slurry to a gravity concentrating step to produce a first underflow and an overflow, subjecting the first underflow to centrifugal separation to yield a second underflow and an overflow, recovering starch from the second underflow, and washing the gluten mass with overflow liquid.

9. Process of preparing wheat starch whic comprises forming a dough containing wheat starch and gluten, working the dough with water to convert said dough into a starch slurry and a gluten mass, separating the starch slurry from the gluten mass, subjecting the slurry to a gravity concentrating step to produce a first underflow 'and an overflow, subjecting the first underflow starch and gluten, working the dough with water to convert said dough into a starch slurry and a. gluten mass, separating the starch slurry from the gluten mass, concentrating the starch slurry bygravity into a thickened underflow and an overflow,- filtering the underflow to recover starch therefrom, washing the gluten with overflow liquid, and then washin the resultant gluten jecting the first overflow to a gravity. separation to yield a third underflow and a third overflow, and returning thethird underflow to the gravity concentrating step.

. 6. Process of preparing wheat starch which comprises forming a dough acontaining wheat ,j-gstarch andgluten, working the dough with water yto convert said doughinto a starch slurry and with filtrate from said underflow.

11. Process of preparing wheat starch which comprises forming a dough containing wheat starchand gluten, working the dough with water to convert said dough into a starch slurry and a gluten mass, separating the starch slurry from the gluten mass, subjecting the slurry to a gravity concentrating step to produce afirst underflow and a first overflow, subjectingthe first under-- flow to centrifugal separation to yield a second underflow and a second overflow, returning the second overflow to the gravity concentrating step, subjecting the first overflow to a gravity separation to yield a third underflow and a third overflow, Washing the gluten mass with the third overflow, filtering the underflow to recover starch therefrom, and washing the preliminarily washed gluten with filtrate from the underflow.

12. Process of preparing wheat starch which comprises forming a dough containing wheat starch and gluten, working the dough with water to convert said dough into a starch slurry and a gluten mass, separating the starch slurry'from' the gluten mass, subjecting the slurry to a gravity concentrating step to produce a first underfiow and a first overflow, subjecting the first underflow to centrifugal separation to yield a second underflow and a second overflow, returning the second overflow to the gravity concentrating step, subjecting the first overflow to a gravity separation to yield a third underflow and a third overflow, washin the gluten mass with the third overflow, filtering the second underfiow to recover starch therefrom, washing the preliminarily washed gluten with filtrate from the second underfiow, returning the third overflow from the gluten washing step tothe dough working step,

and recovering solubles from the third overflow.

ROBERT W. CALLAGHAN. H. SCHILLING.

REFERENCES crrEn The following references are of record in the file of this patent:

UNITED STATES PA'I'ENTS Number Name Date 2,149,802 Thurber Mar. 7, 1939 2,018,668 Peltzer Sept. 10, 1935 2,186,037 Peltzer Jan. 9, 1940 2,097,531 Peltzer Nov. 2, 1937 2,323,077 Peltzer June 29, 1943 2,316,807 Peltzer Apr. 20, 1943 1,585,452 Widmer May 18, 1926 OTHER REFERENCES Starch-Eamon 8r Lane, Cambridge, 1928. (Copy in Div. 43, Des. 144-147.) 

